RFR: 8010385: build with LOG=trace broken on mac

[Erik Joelsson]

The log level 'trace' is broken on both mac and solaris. When trace is 
used, the shell variable is overridden to do the following:

1. Add -x to echo each line that gets executed. This causes all $(shell) 
expressions to be printed in addition to recipes.
2. Add some text explaining if it's a $(shell) or a recipe, what rule it 
belongs to and what triggered it.
3. Add /usr/bin/time to each line and print the output to a special log file

What's failing on Mac and Solaris is 3 since the formatted output and 
ability to print to a separate file is only available in GNU time. On 
Solaris 1 is also failing due to the default shell, /bin/sh, not seeming 
to like this.

I solved 1 by overriding the shell with /bin/bash. We already require 
bash for configure so this should be safe.

For 3, if we don't have GNU time, we can't use the feature, so I let 
configure check for this and disable it if not found.

http://cr.openjdk.java.net/~erikj/8010385/webrev.root.01/

/Erik